Research will be carried out on compounds that inhibit the deaminations of the antitumor agents, arabinosylcytosine and arabinosyladenine. Specifically, adenosine deaminase and cytidine deaminase will be purified from murine tumors and/or murine tissues for enzymatic studies at the molecular level. These enzymatic studies will be used to design and carry out survival studies in tumor bearing mice treated with drug combinations of nucleoside analogs and deaminase inhibitors. In addition, enzymatic, metabolic, and murine survival studies will be done with the 3', 5'-cyclic phosphate derivative of methylthioinosine utilizing murine tumors resistant to the nucleoside due to lack of adenosine kinase activity.